This invention relates to novel polymers containing grafted bis(sulfonyl)amide lithium or sodium salts, methods of preparation thereof and uses thereof as electrolytes in lithium or sodium batteries.
More specifically, this invention relates to novel polymer electrolytes obtained from commercially available polymers as well as novel lithium polymer or sodium polymer-type batteries.
Lead batteries have been the most commonly used for many decades. However, lead technology has numerous disadvantages associated with the weight of the batteries, the toxicity of the lead as well as the use of a corrosive liquid. This has led to the development of alkaline batteries, the electrodes of which are based on nickel and cadmium (nickel-cadmium batteries), or, more recently, based on nickel and metal hydrides (nickel-hydride batteries), or based on silver oxide coupled with zinc, cadmium or iron. All of these technologies use a potassium hydroxide solution as the electrolyte and have as a major disadvantage a relatively low mass energy density with regard to needs associated with the development of portable equipment such as telephones and computers. Moreover, the weight of these batteries is a disadvantage in terms of their use in electric vehicles.
Manufacturers have therefore developed a new line based on lithium batteries using a negative electrode based on carbon, into which the lithium is inserted, and a metal oxide, in particular cobalt, with a high oxidation potential as a positive electrode. The principle of operation is as follows:
During electrochemical charging of the battery, the lithium ions pass through the electrolyte, which is an ion conductor and electronic insulator and is intercalated in the negative electrode material generally formed by graphite during discharging of the battery; that is to say that, during use, it is the reverse phenomenon that occurs. The lithium ions are deintercalated.
In the batteries, the ion conductor or electrolyte, which separates the electrodes, is a key element. On the one hand, its state, liquid, solid or gelled, affects the safety of the system, and, on the other hand, its conductivity determines the operating temperature range.
In lithium batteries, liquid electrolytes based on an organic solvent, such as dimethylenecarbonate or ethylenecarbonate, and a dissolved salt, such as lithium hexafluorophosphate LiPF6 or lithium bis (trifluoromethanesulfonyl) imidide (CF3SO2)2NLi, are commonly used. However, they do not have the optimal safety conditions associated with the handling of a corrosive and flammable liquid. Moreover, these systems have the disadvantage of being capable of forming dendrites during battery charging, which may cause a short circuit and destruction of the battery.
To overcome these major disadvantages, a new technology has been developed, based on solid lithium anode polymer electrolytes, resulting in the name “lithium polymer battery”. Thus, patent FR 2853320 describes electrolytes obtained by polymerization of polyorganosiloxanes by a photoinitiator in the presence of an electrolyte salt. Aside from the fact that the anion is not immobilized and migrates into the electrolyte causing polarization phenomena at the electrodes, this technique requires iodonium catalysts, which are particularly toxic. Thus Chung-Bo Tsai, Yan-Ru Chen, Wen-Hsien Ho, Kuo-Feng Chiu, Shih-Hsuan Su describe, in the patent US 2012/0308899 A1, the sulfonation of PEEK into SPEEK and the preparation of the corresponding lithium salt. This simple technique does not make it possible to have sufficient delocalization of the negative charge on the sulfonate function and the lithium ion is too coordinated with the sulfonate function to reach very high conductivities. More recently, another approach was described by some authors who attempted to immobilize the anion by polymerization of monomers containing the lithium salt serving as the electrolyte. The patent FR 2979630 and the publication of D. Gigmes et al. in Nature Materials, 12, 452-457 (2013) describe the synthesis of block copolymers containing an electrolyte, the anion of which is bound to the polymer. The conductivities indicated are the best obtained so far for lithium polymer batteries. In the synthesis of this type of electrolytes, the starting monomers are not commercial and must be prepared in several steps. Moreover, the polymerization technique for preparing block polymers is costly compared to other polymerization techniques.